1. Field of the Invention
the invention relates to a method for operating a lamp, particularly a lamp for medical applications, having at least one discharge lamp which is connected to a supply unit (EVG) which receives electrical energy from a power supply system having an additional safety power supply (ZSV), the emergency power function prompting a changeover to a standby power source in the event of a fault in the power supply, and, after elimination of the fault, prompting a changeover to the power supply for normal operation. In addition, the invention relates to a failsafe lamp, particularly a lamp for medical applications.
2. Discussion of the Prior Art
A power supply system having an additional safety power supply (ZSV) is defined in VDE Regulation VDE 0107; besides the customary mains power supply, the power supply system comprises a standby power source, which is usually supported by a storage battery.
German reference DE 38 07 585 A1 discloses a surgical lamp which has a high-pressure gas discharge lamp as a light source. This lamp is connected to a supply circuit having an emergency power function, whose input can be connected to a DC voltage source having a lower voltage than the operating voltage of the discharge lamp. It comprises a plurality of first voltage converters for transforming the input voltage into the operating voltage of the discharge lamp, whose inputs are connected in parallel and whose outputs are selectively connected in parallel or in series. The multiplicity of voltage converters means that this is a relatively complex desing.
ln addition. German reference DE 195 05 925 A1 (according to U.S. Pat. No. 5,743,628) discloses a medical lamp, particularly a surgical lamp, which has at least one halogen incandescent lamp and one discharge lamp (halogen metal vapor high-pressure lamp) in its housing. In the event of a failure or fault in the static power supply provided for operating the lamp, the supply of power to the lamp is changed over to a standby power source supported by a storage battery, The radiation from the halogen incandescent lamps is available virtually without interruption on account of the thermal inertia of their coil, whereas the discharge lamp is not available for renewed ignition and startup until after a certain cooling phase over a period of several minutes.
The object of the present invention is to provide a lamp of relatively simple design in which continuous discharge lamp operation is possible even during changeover procedures or in the event of brief voltage drops or voltage failures without renewed ignition procedures. In particular, the intention is to provide a practically failsafe lamp.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a method in which, if a fault occurs during changeover to the standby power source, a buffer store outputs electrical energy to operate the discharge lamp.
Besides changing over in the case of pure DC voltage operation or pure AC voltage operation for the power supply system and the additional safety power supply, it is also possible to change over between different current typesxe2x80x94e.g. from AC voltage to DC voltage or from DC voltage to AC voltagexe2x80x94without impairing the lamp operation, particularly the operating parameters of the discharge lamp.
The buffer store provided is advantageously an electrical capacitor which is at least partly discharged during changeover.
This means that, in the case of a fault during changeover or during a brief voltage drop, the buffer store outputs electrical energy for continuous operation of the discharge lamp.
It is found to be advantageous that, even in the event of brief interruptions, continuous lamp operation is possible without interim ignition operations for the discharge lamp. This means that no inconvenient ignition attempts are made for the discharge lamp during operation. Furthermore, the normal lighting values are quickly restored after the occurrence and elimination of faults. A further advantage can be seen in that the useful life of the lamp is improved on account of reduced loading due to fewer ignition procedures.
In one preferred embodiment of the method, the electrical energy supplied to the supply unit (EVG) first passes through a full-wave rectifier and subsequently a voltage converter containing the buffer store. Energy is subsequently supplied to the discharge lamp via a power-regulated inverter as the output stage.
It is found to be particularly advantageous that the power regulation results in a changeover both from alternating current to direct current and from direct current to alternating current having no effect on the operation of the discharge lamp.
In one preferred embodiment of the invention, while the buffer store is discharging, the discharge lamp is operated in the lower power range for stable illumination (simmer operation). Furthernore, even in the event of a failure in the region of the discharge lamp, at least a certain level of safety should be providedxe2x80x94e.g. in the case of medical application or in the course of a surgical procedurexe2x80x94by virtue of at least standby illumination being ensured by at least one halogen incandescent lamp after an operating fault in the discharge lamp circuit. In the event of a fault in the operation of the discharge lamp or its energy supply, the supply unit (EVG) is used to complete a circuit for operating at least one halogen incandescent lamp. In this context, it is found to be advantageous that an automatic changeover occurs without any significant interruption in the lamp operation.
In addition, in one preferred embodiment of the invention, the operating parameters of the lampxe2x80x94such as starting procedures or illumination time of the discharge lampxe2x80x94are determined using a digital computer and are possibly indicated for monitoring purposes. It is found to be advantageous that the user may actually be referred ahead of time to any relevant measures for reliable operation of the lamp.
Another aspect of the invention resides in the supply unit (EVG) having a buffer store which, in the event of a fault occurring or in the event of a fault being eliminated, is provided for outputting electrical energy for operating the discharge lamp during changeover to the standby power source or during changeover to the power supply for normal operation.
The buffer store used is advantageously an electrical capacitor, so that, in the case of a fault during changeover or during a brief voltage drop, the capacitor outputs electrical energy for continuous operation of the discharge lamp.
It is found to be advantageous that, even in the event of brief interruptions, continuous lamp operation is possible without interim ignition operations for the discharge lamp, and no inconvenient ignition attempts are made for the discharge lamp during operation.
In one preferred embodiment of the invention, a full-wave rectifier is provided at the input of the supply unit for the lamp. The output of the full-wave rectifier is connected to a power-regulated inverter via a voltage converter in order to supply the discharge lamp.
It is found to be particularly advantageous that due to the power regulation of the inverter means, changing over the current type (e.g, alternating currentxe2x80x94direct current) does not result in any impairment of the operation of the discharge lamp.
To maximize its stored energy, the capacitor is preferably arranged in a DC voltage intermediate circuit of the supply unit. The intermediate circuit operates at an operating voltage in the range from 300 to 400 V and forms, together with a step-down converter connected downstream, a DC voltage converter which is connected via the power-regulated inverter to the discharge lamp for the purpose of supplying energy thereto. In terms of its own energy supply, the DC voltage intermediate circuit is connected to the power supply system via a mains filter, a synchronous rectifier connected upstreain of the filter as a full-wave rectifier and via a safety switch. A particular advantage is found to be low-loss operation of the circuit through synchronous rectification and regulation of the power factor.
In addition, in the preferred embodiment of the lamp, an internal auxiliary power supply is provided, with any faults in the external power supply system being detected by a voltage sensor in the region of the mains filter. The voltage sensor preferably has a comparator for detecting faults. In one preferred embodiment, the auxiliary power supply is fed from the buffer store over time.
For its part, the internal auxiliary power supply is connected to the DC voltage converter (step-down converter), to the inverter (output stage) and to a control unit and a data interface. For its part, the control unit is connected to the voltage sensor, to the DC voltage converter (step-down converter), to the data interface and to a reserve lamp controller, in order to be able to change to at least one halogen incandescent lamp in the event of a fault in the operation of the discharge lamp. The halogen incandescent lamp then being connected to the power supply system, including the additional safety power supply (ZSV), and being supplied directly from there.
In one preferred embodiment of the lamp, the discharge lamp is held in a holder which forms, with an inter for the lamp, a structural unit having a universal electrical connection between the igniter and the holder without any internal detachable connecting elements for the lamp. The result of this is, advantageous, low susceptibility to faults.
It is found to be advantageous that symmetrical ignition pulses mean that these ignition pulses travel outwards to the discharge lamp largely without losses and without any electromagnetic interference radiation, despite their large amplitude. Hence, there is also good electromagnetic compatibility in respect of electronic devices in the lamp""s surroundings (EMC).
Advantageously, the structural unit comprising the igniter and the lamp is in the form of a lamp handle or support bracket connected to the holder of the discharge lamp. This refinement makes it possible to achieve a largely compact, easy to maintain design for the complete lamp.
In addition, a useful life indicator is advantageously provided for the discharge lamp, covering illumination duration and the number of ignition procedures.
An operating unit for adjusting and indicating lamp functions can be connected to the data interface connected to the control unit, so that optimum information is ensured.
In a further advantageous embodiment, the lamp according to the invention is provided with an inclination switch. It is found to be advantageous that any inclination into unwanted operating positions results in the lamp immediately being switched off, preventing thermal overloading of components.
A further advantage can be seen in that the surgeon can, if necessaryxe2x80x94e.g. in the case of a minimally invasive or endoscopic method of treatmentxe2x80x94, switch off the lamp by means of sterile operation on the handle (which is sterile anyway) using the inclination switch, where the bright light would interfere with the surgical lamp.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.